The method serves for cutting along predetermined cutting lines, flat objects being conveyed continuously and in parallel to their main surfaces whereby the cutting lines are parallel to the conveying direction. The method is particularly suitable for cutting flat objects which are difficult to be cut because they are e.g. easily deformable and/or consist of several possibly easily deformable layers which layers adhere to each other only slightly. Multi-page printed products made of relatively thin paper are an example for this kind of flat objects.
Flat objects are normally cut or trimmed in a direction perpendicular to their main surfaces. They are e.g. positioned between two straight cutting edges being positioned in a plane perpendicular to the main surfaces and being moved past each other and crossing each other such that the crossing point of the two cutting edges in which point cutting actually takes place moves along the predetermined cutting line across the main surfaces of the object to be cut. Hereby, one of the two cutting edges may lie in the plane of a surface supporting the object to be cut or be a part of this supporting surface. The other cutting edge is then moved relative to the supporting surface, either by being swiveled about an axis or in a movement perpendicular to the supporting surface. Thereby, the one cutting edge moving relative to the support surface is oriented at an angle to the support surface (cutting angle). This kind of cutting method is called cross cutting and is best known as shearing cut of stationary objects.
Devices for cross cutting flat objects being continuously conveyed perpendicular to their main surfaces are e.g. known from the publication EP-367715, devices for cutting flat objects being conveyed in parallel to their main surfaces e.g. from the publication U.S. Pat. No. 3,069,952 or from the publication EP-0698451. If cutting lines of objects being conveyed in parallel to the their main surfaces are perpendicular to the conveying direction the two cutting edges are arranged perpendicular to the conveying direction also. For such a cutting process, a finite time is needed and therefore, for achieving a high cutting precision it is obviously necessary to move the cutting device, at least during the cutting process, together with the object to be cut.
It shows that for cutting lines parallel to the conveying direction and conveyance in parallel to the main surfaces of the objects to be cut, a relative movement of the object to be cut and the cutting edges parallel to the conveying direction and friction forces created by such movement can have a negative effect on the cutting quality. This negative effect can be suppressed by pressing the objects to be cut against a support surface, at least during the cutting process. Such pressing e.g. prevents the object to be cut from being deformed by the relative movement and friction forces or if it consists of layers hardly adhering to each other the pressing prevents these layers from being shifted relative to each other and from such rendering the cut inaccurate.
According to publication EP-0698451, the attempt is made to prevent the above described relative movements between a continuously conveyed object and the cutting edges by moving at least one cutting edge together with the object to be cut in conveying direction. For cutting parallel to the conveying direction, flat objects conveyed in parallel to their main surfaces, this publication suggests to use two cutting blades with straight cutting edges facing each other and to move at least one of these blades with the help of two cranks, whereby a part of the thus created cyclic blade movement is exploited as cutting travel (perpendicular to the conveying direction) and as conveying travel (in conveying direction).
In the same publication it is postulated that the cutting quality achievable with the cutting device as described is best when the speed of the blade conveying travel is approximately the same as the conveying speed of the object to be cut, i.e. when during cutting, relative movements in conveying direction are prevented as far as possible. However, because of the conveying travel being created by the cranks changes sine-like the above condition can, if at all, only be fulfilled during a very short time. Therefore, either the cutting process must be restricted to a correspondingly short time, i.e. the cutting angle (angle between the two cutting edges involved in the cutting process) must be made very small, or a larger relative movement between the cutting edge and the object to be cut must be accepted, both of which facts restrict the application of the described device.
It is the object of the invention to create a method for cutting between two blades and along predetermined cutting lines, flat objects conveyed continuously and at a constant conveying speed substantially in parallel to their main surfaces, whereby a first cutting edge lies in the plane of a support or conveying surface of an object to be cut and the second cutting edge is moved past the first cutting edge and advantageously crosses it. The inventive cutting method is to enable sufficient to very high cutting qualities at low pressing forces by suitable guidance of at least the second cutting edge. In particular, the inventive cutting method is to make it possible to cut accurately and with a satisfying cutting quality objects which are difficult to be cut (e.g. objects which are easily deformable and/or consist of layers which adhere only slightly to each other) without the necessity of high pressing forces as needed in methods according to the state of the art and possibly having a negative effect on sensitive objects. All the same the cutting parameters, especially the cutting angle and the cutting speed are to be freely choosable within wide ranges, i.e. the method is to be simply adaptable to the most various applications.
Furthermore, it is the object of the invention to create a device for carrying out the method which device can be realized and operated with the most simple means.
The invention bases on the finding that it is possible to cut printed products consisting of a plurality of pages with satisfying to very high cutting quality although pressed onto a support surface with very slight pressure only or even without pressure, if in every moment of the cutting process at least the one point of the second cutting edge, which is involved in the cutting process (crossing point with the first cutting edge or cutting point), has a speed relative to the object to be cut which is directed as precisely perpendicular as possible to the support surface or to the first cutting edge or towards the main surfaces of the object to be cut respectively. This means that it is sufficient for only this cutting point of the second cutting edge to have an absolute speed having a component in conveying direction as precisely identical to the conveying speed as possible.
According to the inventive method, at least the second cutting edge which is moved towards the support surface is moved in a manner matched to the continuos conveying of the objects to be cut such that in each moment of the cutting process, at least the cutting point of this cutting edge has a speed of which the component in conveying direction is of the same size as the constant conveying speed. Due to this the friction forces in conveying direction mentioned further above, which friction forces have an accelerating or decelerating or in any case a destabilizing effect on the printed products to be cut, are prevented such that their effect does not have to be counteracted by pressing.
For the purpose of generalization it is stated that for the case in which the first cutting edge is arranged in the plane of the support surface as is suggested in the preceding paragraphs the products to be cut lie against this support surface and against the first cutting edge also due to gravity. Arrangements orientated differently in relation to gravity are thinkable. In such arrangements the named effect of gravity is to be taken over by suitable supporting means. These supporting means have the function of supporting the products such that they lie against the first cutting edge and advantageously against a support surface of which the first cutting edge is a part.
The desired movement of the second cutting edge past the first cutting edge and advantageously crossing the first cutting edge can be most easily realized by swiveling at a constant speed the second cutting edge about a rotation axis arranged above the support surface, whereby the rotation axis is perpendicular to the plane in which the two cutting edges are arranged and move. As will be shown further below the above condition can be fulfilled in this kind of arrangement by matching the distance between the rotation axis and the support surface and/or the rotation speed with the conveying speed. The cutting speed, i.e. the speed with which the cutting point moves on the main surfaces of the object to be cut, is dependent on the rotation speed and on the position of the swiveling second cutting edge in relation to the rotation axis. This position is freely selectable within a large range.
The inventive device for carrying out the embodiment of the inventive method described above comprises a pair of blades orientated in conveying direction each having a substantially straight cutting edge. The first cutting edge is arranged in the plane of the support surface of the object to be cut, the second cutting edge is swivelable or rotatable about a rotation axis positioned above the support surface. The second cutting edge is positioned in a plane perpendicular to the rotation axis. In an advantageous embodiment, a plurality of blades with second cutting edges are arranged on a uniformly rotating carrier.
Further embodiments of the inventive method comprise movement of the second cutting edge past the first cutting edge in a direction perpendicular to the support surface or in a rotation movement about a rotation axis lying in the plane of the support surface and simultaneous movement in conveying direction at a constant speed identical to the conveying speed. In such a case, again in every moment of the cutting process, not only the cutting point on the second cutting edge but the whole cutting edge has a speed relative to the object to be cut which is orientated precisely perpendicular to the support surface.
It shows that in many applications it is sufficient for the first cutting edge arranged in the plane of the support surface of the objects to be cut to be stationary. However, this cutting edge may be moved also such that there is as little relative movement as possible between the first cutting edge and the objects to be cut.